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Old 01-09-2008, 08:58 PM
Ian Campbell
 
Default d-i support for running in a Xen guest domain

Hi,

Firstly apologies for the cross post but I think this genuinely is of
interest to both audiences. I'm subscribed to both lists so no need to
CC me.

I'm interested in getting d-i to work seamlessly inside a Xen guest
domain using the paravirt_ops kernel support for Xen in 2.6.24+
(currently only available in the kernel svn trunk snapshots builds I
think).

At the moment the normal way to deploy a Debian VM seems to be to use
debootstrap. However this has short comings WRT non-Debian domain0, plus
the installer way of doing things is more more familiar to many (well,
IMHO) and d-i sets up a bunch of stuff which otherwise has to be done
manually (packages such as xen-tools help with that bit though). Making
d-i available for PV use also allows the virtual machines to appear more
like native machines to an admin and the installed result is more like a
regular Debian install. FWIW several other distros support using their
installer in a PV context (Fedora, RHEL and SLES that I'm aware of).

I've built myself a Xen-enabled netboot image and didn't come across any
major issues or show-stoppers, just small niggles, such as allowing grub
to run successfully inside a PV domain (patches in: grub #456776,
grub-pc #456777 and grub-installer #456784).

The only real stumbling block at the moment is the kernel. Most
distributions (including Debian) only support PAE Xen on i386 but the
d-i kernel is non-PAE. I don't imagine there would be much enthusiasm
about enabling PAE in d-i so I think at least one new d-i flavour would
be required here.

It would be reasonably easy to create -xen-686 udebs (in fact I did for
my testing) and tweak d-i to select a -xen kernel package image as
appropriate during install, however I think I have a better idea ;-)...

I'd like to propose enabling Xen guest support in all the native i?86
kernel images (and eventually amd64 too), or at least in the -686-bigmem
kernel. Since paravirt ops is already enabled in all kernels (for KVM
and lguest) there is only minimal additional overhead to enabling Xen.

As a nice bonus this would also allow the separate -xen flavour kernels
to be removed/deprecated which seems like a good thing in the
paravirt_ops based world.

Given a suitable kernel it would then be possible to add a -bigmem
flavour of d-i. That would give us installer images which support
native, Xen, KVM and lguest via paravirt_ops both PAE and non-PAE
allowing Debian to be installed as a guest on a wide variety of domain0
distributions.

So, what do the kernel folks think about enabling Xen guest support in
all kernels where it is available and getting rid of the -xen specific
variants? I've got a massive (mainly due to lots of deletion) patch
against SVN which does just that, if there is interest I'll work out the
kinks and file it as a wishlist bug.

And what do the d-i folks think about an additional d-i flavour for
-686-bigmem? Initially I'd propose just building a netboot type image. I
don't think cdrom or floppy are all that critical in a virtualised
scenario, although CD support would be a nice to have, I suppose. I've
got some hacky patches but they would likely need change depending on
the decision made WRT the kernel.

For those who are interested the only other issues I've come across
while playing with this is the need to run a getty on /dev/hvc0 and
breakage with update-grub with the latest xen enabled kernels due to the
CONFIG_* change since 2.6.18. Seems like both should be easy enough to
fix...

Cheers,
Ian.
--
Ian Campbell

There has been a little distress selling on the stock exchange.
-- Thomas W. Lamont, October 29, 1929 (Black Tuesday)
 
Old 01-09-2008, 10:59 PM
maximilian attems
 
Default d-i support for running in a Xen guest domain

On Wed, Jan 09, 2008 at 09:58:45PM +0000, Ian Campbell wrote:
<snipp d-i side>
> I'd like to propose enabling Xen guest support in all the native i?86
> kernel images (and eventually amd64 too), or at least in the -686-bigmem
> kernel. Since paravirt ops is already enabled in all kernels (for KVM
> and lguest) there is only minimal additional overhead to enabling Xen.
>
> As a nice bonus this would also allow the separate -xen flavour kernels
> to be removed/deprecated which seems like a good thing in the
> paravirt_ops based world.

this sounds like a good plan, getting rid of the number of images
is always a welcome bonus.

i know that fedora also is very keen to move to the paravirt_ops world.
for Etch linux-2.6 had dom0 images, when will those be merged,
where are the patches based on paravirt ops against 2.6.24?
we wouldn't want to release Lenny without the support we had given
in Etch (which turned out to be *very* buggy, but that is another
story) of a dom0 linux-2.6 linux-image variant.

> Given a suitable kernel it would then be possible to add a -bigmem
> flavour of d-i. That would give us installer images which support
> native, Xen, KVM and lguest via paravirt_ops both PAE and non-PAE
> allowing Debian to be installed as a guest on a wide variety of domain0
> distributions.

linux-2.6 already builds the -bigmem flavour and afaik it is instelled
by d-i later but not used on boot.

> So, what do the kernel folks think about enabling Xen guest support in
> all kernels where it is available and getting rid of the -xen specific
> variants? I've got a massive (mainly due to lots of deletion) patch
> against SVN which does just that, if there is interest I'll work out the
> kinks and file it as a wishlist bug.

2.6.24 is right now open for such changes,
thanks for your already filed and fixed virtualization i386 bug report,
had gone unnoticed for a while as focus slipps to amd64.

happy hacking

--
maks


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Old 01-10-2008, 11:37 AM
Bastian Blank
 
Default d-i support for running in a Xen guest domain

On Wed, Jan 09, 2008 at 09:58:45PM +0000, Ian Campbell wrote:
> I'm interested in getting d-i to work seamlessly inside a Xen guest
> domain using the paravirt_ops kernel support for Xen in 2.6.24+
> (currently only available in the kernel svn trunk snapshots builds I
> think).

2.6.23 already have the same amount of support than .24.

> It would be reasonably easy to create -xen-686 udebs (in fact I did for
> my testing) and tweak d-i to select a -xen kernel package image as
> appropriate during install, however I think I have a better idea ;-)...

The explicit Xen images will disappear in the future, it just lacks
infrastructure.

Bastian

--
Yes, it is written. Good shall always destroy evil.
-- Sirah the Yang, "The Omega Glory", stardate unknown


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Old 01-12-2008, 04:30 PM
Ian Campbell
 
Default d-i support for running in a Xen guest domain

On Thu, 2008-01-10 at 00:59 +0100, maximilian attems wrote:
> On Wed, Jan 09, 2008 at 09:58:45PM +0000, Ian Campbell wrote:
> <snipp d-i side>
> > I'd like to propose enabling Xen guest support in all the native i?86
> > kernel images (and eventually amd64 too), or at least in the -686-bigmem
> > kernel. Since paravirt ops is already enabled in all kernels (for KVM
> > and lguest) there is only minimal additional overhead to enabling Xen.
> >
> > As a nice bonus this would also allow the separate -xen flavour kernels
> > to be removed/deprecated which seems like a good thing in the
> > paravirt_ops based world.
>
> this sounds like a good plan, getting rid of the number of images
> is always a welcome bonus.

I have build tested the attached patch and test booted the -486 and
-686-bigmem versions on native.

Unfortunately the Xen domain builder isn't capable of loading a native
bzImage directly -- it requires the ELF vmlinux. I hacked
around that when I was playing with Xen enabled d-i and
then promptly forgot I had done so, which is a shame because it's quite
important! For now I grabbed the 686-bigmem vmlinux from the build tree
and boot tested that.

People were looking at modifications to the kernel and/or the Xen
domain builder to allow it to boot a bzImage, I think by making the
bzImage payload be an ELF file instead of the current raw binary blob.
I'll see what is going on in that area.

I don't think there is any harm in applying the patch now, although
without a patch for builder support it's a bit pointless.

> i know that fedora also is very keen to move to the paravirt_ops world.
> for Etch linux-2.6 had dom0 images, when will those be merged,
> where are the patches based on paravirt ops against 2.6.24?
> we wouldn't want to release Lenny without the support we had given
> in Etch (which turned out to be *very* buggy, but that is another
> story) of a dom0 linux-2.6 linux-image variant.

The Fedora guys announced that they were working on dom0 paravirt_ops
stuff at the end of last year [0]. I must admit I haven't really been
keeping up with their efforts though.

I had a dig around and didn't see anything further to what was
announced. They were targeting Fedora 9. According to [1] feature freeze
is start of March so I'd presume they plan to have patches before then.

[0] https://www.redhat.com/archives/fedora-xen/2007-November/msg00106.html
[1] http://fedoraproject.org/wiki/Releases/9

Cheers,
Ian.
--
Ian Campbell

From the cradle to the coffin underwear comes first.
-- Bertolt Brecht
 
Old 01-12-2008, 04:30 PM
Ian Campbell
 
Default d-i support for running in a Xen guest domain

On Thu, 2008-01-10 at 13:37 +0100, Bastian Blank wrote:
> On Wed, Jan 09, 2008 at 09:58:45PM +0000, Ian Campbell wrote:
> > I'm interested in getting d-i to work seamlessly inside a Xen guest
> > domain using the paravirt_ops kernel support for Xen in 2.6.24+
> > (currently only available in the kernel svn trunk snapshots builds I
> > think).
>
> 2.6.23 already have the same amount of support than .24.

That's true. I'm not sure why I thought otherwise.

> > It would be reasonably easy to create -xen-686 udebs (in fact I did for
> > my testing) and tweak d-i to select a -xen kernel package image as
> > appropriate during install, however I think I have a better idea ;-)...
>
> The explicit Xen images will disappear in the future, it just lacks
> infrastructure.

By infrastructure do you mean meta-packages to facilitate upgrade or
something else?

Ian.
--
Ian Campbell

And ever has it been known that love knows not its own depth until the
hour of separation.
-- Kahlil Gibran
 
Old 01-13-2008, 12:44 PM
Bastian Blank
 
Default d-i support for running in a Xen guest domain

On Sat, Jan 12, 2008 at 05:30:20PM +0000, Ian Campbell wrote:
> > The explicit Xen images will disappear in the future, it just lacks
> > infrastructure.
> By infrastructure do you mean meta-packages to facilitate upgrade or
> something else?

Infrastructure as in maintainer scripts.

Bastian

--
Killing is wrong.
-- Losira, "That Which Survives", stardate unknown


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Old 01-14-2008, 03:56 PM
maximilian attems
 
Default d-i support for running in a Xen guest domain

On Sat, 12 Jan 2008, Ian Campbell wrote:

> Unfortunately the Xen domain builder isn't capable of loading a native
> bzImage directly -- it requires the ELF vmlinux. I hacked
> around that when I was playing with Xen enabled d-i and
> then promptly forgot I had done so, which is a shame because it's quite
> important! For now I grabbed the 686-bigmem vmlinux from the build tree
> and boot tested that.

hmm there were the xen images i guess they did something similar,
maybe look there on how to grab them with maintainer scripts.

so enabling won't bring us much for now also due to !pae i only see
a current value in i386 bigmem.

> The Fedora guys announced that they were working on dom0 paravirt_ops
> stuff at the end of last year [0]. I must admit I haven't really been
> keeping up with their efforts though.
>
> I had a dig around and didn't see anything further to what was
> announced. They were targeting Fedora 9. According to [1] feature freeze
> is start of March so I'd presume they plan to have patches before then.

referring to that:
http://fedoraproject.org/wiki/Features/XenPvops
(seem to not load right now on my end, but should be the page)


amicalement

--
maks


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Old 02-03-2008, 08:43 AM
Ian Campbell
 
Default d-i support for running in a Xen guest domain

On Sat, 2008-01-12 at 17:30 +0000, Ian Campbell wrote:
>
> Unfortunately the Xen domain builder isn't capable of loading a native
> bzImage directly -- it requires the ELF vmlinux. I hacked
> around that when I was playing with Xen enabled d-i and
> then promptly forgot I had done so, which is a shame because it's
> quite important! For now I grabbed the 686-bigmem vmlinux from the
> build tree and boot tested that.

Took me a while but there is now a patch queued with upstream which
fixes this issue
http://git.kernel.org/?p=linux/kernel/git/x86/linux-2.6-x86.git;a=commit;h=23eea6d21020dfaa740c01b911f46a9 5505c9b37
would a backport to 2.6.24 be applied by Debian?

I'm working on the domain builder bits on the Xen side at the moment.

Ian.
--
Ian Campbell

When in doubt, mumble; when in trouble, delegate; when in charge, ponder.
-- James H. Boren
 

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